This invention pertains to an improved treated catalyst material useful for hydroconversion of hydrocarbon feedstocks containing high concentrations of metals-containing compounds. It pertains more particularly to a frangible catalyst comprising porous aluminum oxide promoted with metal oxides, and to a method for pretreating the catalyst material to make it more resistant to attrition during subsequent use and provide more stable operations in a hydrocarbon catalytic ebullated bed demetallization process.
Bauxite, a naturally-occuring low-cost aluminum oxide material when activated and promoted with certain metal oxides, is effective as a catalyst in upgrading heavy petroleum feedstocks having high metals content in an ebullated-bed reactor, provided that the catalyst can show satisfactory fluidization patterns and acceptable catalyst attrition rates in the reactor. For example, U.S. Pat. Nos. 3,901,792 and 3,964,995 to Wolk, et al., disclosed a two-stage process for demetallization and hydroconversion of high-metal content petroleum residuum feedstocks such as those obtained from Canada, Iran, and South America. The first stage reactor contained a porous bauxite catalyst material which contained promoters of metal oxides of iron, silicon and titanium and had a primary purpose of removing the metals such as vanadium and nickel compounds from the hydrocarbon feedstocks. Such demetallization of the feed in the first stage reactor was found to improve the second stage catalytic desulfurization performance significantly.
However, it has been found that some operational problems interfere with stable bed fluidization and sustained operations on metals-containing hydrocarbon feedstocks when using available activated bauxite catalyst material impregnated with metal oxide promoters such as about 0.5-3 W % molybdenum in an ebullated catalyst bed reactor. Typical operational problems encountered with the available 20.times.50 mesh size promoted activated bauxite catalyst were poor ebullation of the catalyst bed and excessive catalyst particle attrition and carryover rates from the reactor, thereby requiring excessive catalyst replacement rates. The poor catalyst bed fluidization patterns in the reactor led to erratic operations, and the high catalyst attrition rate and its subsequent excessive carryover from the reactor caused plugging problems in the reactor liquid recycle conduit and in lines downstream from the reactor. Thus, improvements in ebullated bed reactor operations on hydrocarbon feedstocks when using inherently frangible catalyst materials are needed.